No of reasons can cause this to occur.
- Webmail is not selected for the domain.
- The webmail is selected, but the bindings didn’t get set correctly in IIS.
- There can be an upgrade to the webmail/mail software.
- Log into your Control Panel.
- Click on the Home tab. In the My Subscriptions section select the domain you want to manage.
- Click on the Mail tab. Then click Change Settings.
- In the Webmail drop down select None and click OK.
- Select Mail Settings again.
- In the Webmail drop down select Mailenable and click OK.
Webmail should now be enabled.